The present invention relates broadly to the field of manufacturing equipment and particularly to the field of moving delicate semiconductor wafers from one position to another.
In the field of automated material handling, much has been done to permit automated manufacture of such semiconductor wafers. For example, U.S. Pat. No. 4,030,622 issued June 21, 1977 shows a wafer handling system for transporting delicate silicon wafers into and out of a vacuum chamber. In that system, a vibrating track is used to move the silicon wafer from one position to another. History has proven that the use of vibrational tracks to transport wafers from one location to another is undesirable as the wafers are so fragile that they frequently break while being moved on such vibrational tracks.
A holder device for handling semiconductor wafers is illustrated in the IBM Technical Disclosure Bulletin, Vol. 25, No. 5, Oct. 1982 pages 2334-2335. This holder uses a gripper which only contacts the edge of a wafer and not the active surface of a wafer. The mechanism shown there, however, is disposed over the active surface and has moving members which are in sliding contact with other members thereof. Sliding contact of the members, however, produces minute contamination particles as the pieces rub against each other in normal use. These particles can fall onto the active surface of a wafer disposed below them and cause failures thereon. Accordingly, such an apparatus contributes to reducing the manufacturing yield and for this reason is undesirable. The mechanism is also undesirable because edge contact does cause some breakage of wafers which further contributes to reduced manufacturing yield.
U.S. Pat. No. 4,042,128 issued Aug. 16, 1977 illustrates another wafer transfer apparatus. In this apparatus, there is a substrate carrier with a plurality of standoff supports. A substrate is positioned on the carrier so that the edges thereof rest on a sloping surface of the standoffs. As such, each substrate is supported by only its edge at several points around its circumference. In practice, this support method causes excessive substrate edge breakage which contributes to reduced manufacturing yield and, hence, is not desirable.
U.S. Pat. No. 4,466,766 illustrates yet a further apparatus for transferring wafers from a process carrier to a furnace carrier. As with other transfer devices described earlier, this one engages the edge of the wafer as well which contributes to wafer breakage in the manufacturing processes. It also has mechanisms disposed above the wafers which have sliding contact with other mechanism which may produce tiny metal particles that can fall onto the active surface of the wafer which may result in the formation of a circuit defect. Accordingly, in applications where super clean conditions must be maintained and high manufacturing yield is required, the transfer device of the subject patent is not suitable.
In view of the above noted problems associated with prior art wafer handling equipment, it is the primary objective of the present invention to provide a wafer transfer mechanism which enhances the manufacturing yield.
It is a further objective of the present invention to provide a wafer transfer mechanism which does not does not contribute to wafer breakage.
It is another objective of this invention to provide a wafer transfer device which does not have any elements thereof disposed above the active surface of the wafer which are in sliding contact with any other element thereof thereby eliminating a source of particles which might fall on the active surface and cause a circuit defect.
It is still another objective of this invention to provide a wafer transfer device which can operate in manufacturing equipment where only a small vertical opening is available in which to position and operate the wafer transfer device.